Furnace and method of operating the same



Dec. 17 1929. w. DE FRIES FURNACE AND METHOD OF OPERATING THE SAME Filed April 7, 1921 2 Sheets-Sheet W ACSQZZm-OR. n

Dec. H7, 1929. DE FRIES I FURNACE AND METHOD OF OPERATING THE SAME Filed April 7. 1921 2 Sheets-Shem INVENTQW. W k

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WALTER DE FRIES, 01E WILKKNEJBURG, I EINSYLVANL L FURNACE .lll l'l) METHQZD U15 @PERAE'ING THE SAME application filed April 7,

Figure l is a longitudinal vertical section showing one embodiment of my invention Figure 2 is a section on the irregular line Ill-ll of Figure 1; and

Figure 3 is a section on the line ill-dill of Figure 1.

My invention has relation to furnaces and to the method of operating the same. "While the invention is herein shown and specifically described in connection with a reversing regenerative furnace of the open-hearth type, it is applicable to various other types of furnaces within the scope of my broader claims.

At present, the regenerative Siemens type of furnace is universally employed for the attainment of those high temperatures which are necessary to cause the proper reactions involved in the manufacture of metals, glass and other products. To be regenerative, however, these furnaces naturally have to be reversible, and until recently it has been standard practice to construct their ports with regard to the double function which they have to perform, namely, to serve as passageway both for the incoming and outgoing fuel and gases.

The high temperature of the outgoing gases heats the refractory material forming these ports, their connections leading thereto and the regenerating chambers, of course, to the point of incandescence, and this, in turn, made it necessary to provide separate fuel and air ports, because the temperature of these passageways preheated the incoming fuel and air considerably above the ignition point of their reaction mixture. This has involved the necessity of using the non-explosive fuel combustion method, in which the fuel is introduced into an oxygen-containing atmosphere, the flame-producing reaction between the fuel and air taking place as they meet each other on their travel through the furnace chamber. I

To complete the combustion of the fuel in troduced in this manner into the furnace, the reaction chambers are usually of long rectangular designs, in order to provide ample time for the entering fuel and oxygen-eontaining atmosphere to come in contact with each other. Clhe speed of tieseincoming gases has, of necessity, to be comparatively low, otherwise the desired reaction would not take place in the furnace chamber, and this low speed has resulted in a spreading of the flame, which gradually fills the whole: furnace chamber and imparts heat not only to the bath but to the walls of the chamber from which it is radiated without practical utilization.

Furthermore, it has been found necessary to introduce an excess of oxygen or air (about l0% in good practice) into the furnace to insure the combustion of the fuel within the chamber, which, on the other hand, is a decidedly undesirable factor for the heating or refining operation carried on in the same chamber. 'Where such an oxidizing atmosphere is actually harmful, as for instance, in the last refining stages of the open hearth process, an excess fuel and gas supply is resorted to to eliminate it. involving. thus a waste of fuel in the chamber.

As it is well recognized and well known, on the other hand, that an excess of either fuel or oxygen in the combustible mixture materially decreases the reaction temperature, which, as stated in the beginning, is a prime requisite for the refining process, it was found inevitable to construct checker chambers which gave a maximum preheating effect to offset this loss. With air and gas thus heated to the limit previous to their reaction upon each other, the formation of an explosive mixture was actually effectively prevented.

Recently, attempts have been made to improve this practice and to obtain a more rapid combustion and a more intimate contact between fuel and air by forcing both fuel and air through a common restricted inlet port. While the claim was made that a mixture of fuel and gas results from such practice, it is evident that with both gas and air preheated considerably beyond the ignition temperature of their explosive mixture, such mixture can not be accomplished, as the layers of the hot fuel gas stream nearest to the hot air stream will immediately ignite upon contact with the latter, especially in the presence of the incandescent refractory forming the restricted port, resulting in a non-explosive combustion starting in this port.

The beneficial influence of this improved practice is therefore limited to its high speed flame development and a better heat transfer effect resulting therefrom, together with a reduced radiation loss. A high speed of the entering gases tends to keep the flame in a predetermined shape, preventing the spreading over the area of the furnace chamber, which was referred to above as a disadvantage of the old method.

Other improvements have resorted to in directpreheating of the fuel gas through the medium of preheated air, the fuel and air stream converging into a common port. In all such attempts, however, these ports serve wholly or in part likewise as offtake ports and as such are subject to a high heat which makes a refractory body luminous and causes partial ignition of the entering gases, thus preventing their homogeneous mixture. Furthermore, the destructive action of the outgoing gases tends to destroy the shape of such ports, rendering them gradually less useful as inlet ports or else make the employment of artificial cooling devices necessary.

To offset this latter effect, designs have been invented which permit a removal of the outgoing gases in passages different from those used for the incoming gases, one of them having been described in my previous application filed under Serial No. 427,520. However, in thiscase, the entrance port is still subject to the heat radiation of the connecting furnace chamber, which again'brings the temperature of its refractory body likewise beyond the ignition point of the incoming gases, thus preventing the formation of an explosive fuel-air mixture for the reasons above described.

The object of the present invention is to prevent premature ignition of the incoming gases and thus to obtain in the inlet port an explosive mixture, which is preheated to a point slightly below its ignition temperature and discharged into the furnace through a suitable nozzle at a speed higher than the speed of the flame propagation of the particular mixture to prevent back flashing, and which is finally ignited in the furnace chamber. This results in a short, non-luminous, explosive combustion of fuel, creating temperatures not hitherto obtainable with the non-explosive combustion method above described, and which are more nearly in accordance with the theoretical maximum value of any particular mixture. In this manner, excess oxygen in the furnace chamber can be eliminated and a non-oxidizing atmospheremay be obtained with a neutral flame of high temperature and substantially complete combustion, as compared with incomplete combustion or excess gas atmosphere within the furnace, which is now commonly used for the purpose of preventing oxidation of the charge. Owing to the fact that existing formulae ascribe a better rate of heat transfer to the radiation method than to the convection principle, the belief has prevailed that for efiicient heating, a luminous flamecan not be dispensed with; and open-hearth furnaces have heretofore been built on this basis. In this practice, however, the absorption factor of hot steel in relation to radiant heat is not taken into account. In other words, while the higher heat transfer possibility of a radiant stream of heat is undeniable, the capacity of the hot steel to absorb such radiant heat is an unknown quantity, especially considering the fact that liquid steel itself is luminous. It is probable, that, in fact, only a very small amount of radiant heat, as'compared with the total heat developed, is actually absorbed by the liquid steel which, due to its own luminosity, may give up as much if not more heat by radiation to the furnace walls than it receives by radiation after it becomes luminous. llt is therefore probable that the majority of the heat which is added to the bath after it has been melted down is transferred to it by convection, and the rate of this transfer is favorably influenced by the temperature difference which exists between the source of heat and the bath, and further, by the velocity with which the developed heat passes over the bath. The explosive combustion which is obtained by the practice of my invention with its high temperature heat development, which a proaches the theoretical maximum, coupler with as high a speed of the incoming gases premixed with air for their combustion as is permissible with the ignition propagation rate of any particular mixture, thus gives ideal conditions for the eflicient heat transfer to the bath in openhearth furnaces.

It follows from the above discussion that with the application of my invention to reversing furnaces, inlet ports and outlet ports have to be entirely separated from each other. though they may connect to common inlet and waste gas outlet passages as are necessary for furnaces of this type. This, however, materially simplities the construction of the furnace,

in that it is necessary to provide for only a single regenerating chamber at each end of the furnace.

The invention also makes it possible to reduce the length of the heating chamber and increase its width to obtain a certain area of the bath exposed to the action of the heat. An increased width, however, will permit the installation of a larger number of my burners. through which more heat may be generated for the given furnace area than it-is possible to produce in the present rectangular type of chamber. The result would be a substantial reduction in time now required for the refining operation.

treason While l have shown and described my in vention in connection with a furnace in which gas is used as the fuel element, it will be understood that the invention is equally applicable to liquid fuels and also powdered coal.

In the accompanying drawings, the numeral 2 designates a portion of the melting chamber of an open-hearth furnace. 3 designates a supply main and at an air uptake which leads from the usual air regenerator, not shown. 5 is a gas port leading upwardly from the main 3, and provided with any suitable controlling valve 6. Placed in the port 5 is a temperature-equalizing chamber consisting of a refractory member 7, through which the gas from the port 5 passes and which dis charges into a suction and mixing chamber 8, attached to which is a dischargenozzle 9, forming in connection with the mixing chamber a passage of the familiar Venturi pipe shape. The air uptake 4 is branched at its upper portion, one branch 10 leading upwardly and discharging around the equalizing chamber 7, this branch forming the air inlet port. The other branch 11 leads into the chamber below the discharge from the nozzle portion of the chamber 8, and constitutes the waste gas ofl'take. 12 is a suitable controlling valve placed in the port 10.

\Vhile it is possible with this arrangement of ports to use one of the two parts at each end for the incoming or outgoing gases respectively by creating a strong suction effect in one port which, on the incoming side, for instance, would prevent any preheated air being discharged through the other port into the furnace chamber and vice verse, I preferably employ a sliding damper 13, by means of which either port can be effectively closed. It will be noted that in the position shown in the drawings, the damper 13 is lowered to close the offtake port 1]. When raised, it closes off the inlet port. The provision ofthis damper enables a slight suction, such as it is possible to create lwith the usual available pressure in the fuel mains, to be used with proper results.

The walls of the chambers 8 and 9 are shown as having a coolingjacket 14-. The damper 13 is also shown as of the water-cooled type, and is also provided with water-cooled guides 15. and water-cooled abutments 16.

In the construction shown. the interior of the equalizing chamber is provided with helical blades 17, and the exterior of this chamber is provided with oppositely directed helically arranged blades 18. These are of advantage in effecting a proper mixture of the fuel and air, but may be omitted.

ln the construction shown. the equalizing chamber is comparatively short. This is due to the fact that the drawing shows a furnace in which raw producer gas is employed. This producer gas is usually supplied at about the heat with which it leaves the producer, and comparatively little heat exchange is necessary before the gas'and air may be properly mixe In case of cold gas, however, this regulator or exchanger would have to be materially lengthened to elfeot the proper amount of heat exchange. This would also be the case when liquid or powdered fuel are employed. These are usually fed into the burner from an atomizer, and in such cases, the hot refractory walls of the equalizing chamber serve not only the purpose of temperature equalization, but also as a means for changing the fuel vapors or p0wders into a fixed gas which may subsequently be properly mixed in the other parts of the burner.

Thus far, I have described Figure 1, as though but a single burner were employed; and, in fact, such single burner will be sufficient for smaller furnaces. My invention, however..contemplates the use of any desired number of these burners placed side by side, as indicated in Figure 2, each of these burners ha ring its own temperature equalizer. air supply port and suction and discharge chamber or nozzle. The one damper 13 may be connnon to all the burners.

lln the operation of the furnace, the air is preheated above the ignition point of the combustible mixture, which is to be formed, in a primary heat exchanger with the heat of the Waste gases of the furnace or other- Wise. In passing through the temperature-equalizing chamber, or secondary heat exchanger, this air gives up its excess heat to the gas passing through the equalizer. The result is that the combustible mixture when formed in the'chamber 8 it at a temperature below the ignition point of the mixture. The volumes of gas and air are regulated as nearly as possible to provide an explosive mixture which on its discharge from the nozzle or nozzles 9. coming in contact with the hot walls of the furnace, gives rise to a short explosive combustion, the discharge being at a speed higher than the flame propagation.

lVhile theoretically similar results to those above described may be obtained by preheating the fuel to a degree above the ignition point of the combustible mixture and causing the transfer of the excess heat from the fuel to the incoming air. in practice, it is more desirable to preheat the air.

It will be noted that by the use of my invention, only a single regenerator is necessary at each end of the furnace, thus greatly simplifying the regenerator and port structures of the furnace. In fact, my invention makes it possible to use recuperators as distinguished from regenerators. This application of my invention will form the subject matter of a separate application. but it will he understood that the broader claims of this application are intended to cover any means .trod'ucing them into operation,

element, and

the ignition temperature of the mixture, substantially as described.

2. The herein described method of furnace operation which consists in separately supplying air and fuel, preheating the air above the ignition temperature of the mixture of air and fuel, utilizing the excess heat of the preheated air to raise the temperature of the fuel, and then bringing the elements together and introducing them into the furnace at a temperature slightly below the ignition point of the mixture and causing ignition to take place within the furnace chamber, sustantially as described.

3. The herein described method of furnace operation; which consists in separately supplying a fuel element and a combustion ele-.

vment, preheating'on'e of said elements above the ignition temperature of the fuel mixture,

utilizing the excess heat of the preheated elementto raise the temperature of the other bringing said elements together in approximately the proportions required to produce an explosive combustion and intially .as described.

4; The herein described method of furnace which consists in separately supv plying air and'fuel, preheating the air above the ignitiontemperature of the fuel and air mixture, utilizing theexcess heat of the preheated air toraisethe temperature of the i'ucland thereby lower the temperature of the air, bringing the air and fuel together in approximately the proportions required for and introducing theexplosive combustion, mixture into the furnace, scribed.

5. The herein described method of furnace operation, which consists in separately supplying air and a fuel, preheating the air above the ignition temperature of the fuel and air mixture, utilizing the excess heat of the preheated air to raise the temperature of the fuel and thereby lower the temperature of the air, and then bringing the air'and substantially'as deffueltogether in approximately the proporintimately mixing them,

tions required for explosive combustion and and then discharging the mixture into the furnace at a temperature at the point of discharge lower than the the furnace, substan the preheated air to raise the temperature of the fuel and thereby lower the temperature of the air, then bringing the fuel and air together at a temperature below the ignition point of the mixture, and discharging the mixture into the furnace through a suitable nozzle at a speed higher than the rate of flame propagation of the mixture, substantially as described. l

7. The herein described method of furnace operation, which consists in separately supplying air and a fuel, preheatingthe' air above the ignition temperature of the fuel and air mixture, utilizing the excess heat of the preheated air to raise the temperature of the fuel and thereby lower the temperature of the air, then bringing the fuel and air together at a temperature below the ignition point of the mixture, discharging the mixture into the furnace through a suitable nozzle at a speed higher than the rate of flame propagation of the mixture, igniting the mixture, causing the Waste gases to escape through a port or passage which is separate and independent of the fuel mixture inlet port, and repeating this process upon reversal of the furnace-substantially as described.

8. The herein described method of regenerative furnace operation, which consists in separately supplying air and fuel, preheating the air, through the medium of a primary heat exchanger, with the waste gases of the furnace above the ignition temperature of the fuel and air mixture, utilizing the excess heat of this preheated air to raise the temperature of the fuel through the medium of a secondary heat exchanger, thereby lowering the temperature of the preheated air, then bringing the fuel and air together at a. temperature elow the ignition point of their mixture, discharging this mixture into the furnace through a suitable nozzle at a speed higher than the rate of flamepropagation of the mixture, igniting this mixture, causing the waste gases to escape through a port of discharge which is separate and independent of the fuel mixture inlet. port, utilizing all or part of the remainingheat of the waste gas for the purpose of raising the temperature of the incoming air in the primary heat exchanger above referred to, and repeating this process upon reversal'of the furnace, substantially as described.

9. A furnace having an intake port, separate air and fuel supplying means discharging into said port, means for preheating the air before it is delivered to said port, and means for utilizing the preheated air to raise III the temperature of the fuel before is mixed with the air, substantially as described.

10. A. furnace having an intake port, sep arate air and fuel supplying means discharging into said port, means for preheating the air before it is delivered to said port, and means for utilizing the reheated air to raise the temperature of the uel before it is mixed with the air, together with a nozzle through which the mixture of air and fuel is dis- Bill charged into the furnace chamber, substantially as described.

ll. A furnace having an inlet port, separate air and fuel supply means discharging into said port, means for preheating the air before it isdel vered to said port, a heat exchanger for utilizing the excess heat of the preheated air to raise the temperature of the fuel and lower the temperature of the air, a mixing chamber for etlectingthe mixture of the fuel and air, and a discharge for such mixture into the furnace chamber, substain tially as described.

12. A furnace having an intalre port, separate air and fuel supply means discharging into said port, means for preheating the air before it delivered to said port, and means for utilizing the preheated air to raise the temperature of the fuel before it is mined with the air, together with a nozzle through which the mixture of air and fuel is discharged into the furnace chamber, said fur nace having an odtalre port which is sepa rate and independent of the inlet port, sub stant-ially as described,

13. A furnace having an inlet port, sepa: rate hi1 and fuel supply means discharging into said port, means for preheating the air before it is delivered to said port, a heat erchanger for utilizing the excess heat of the preheated air to raise the temperature of the fuel and lower the temperature of the air, and a mixing chamber and nozzle for effecting the mixture of the fuel and air and a discharge of such mixture into the furnace chamber, said furnace having an otl'taire port which is separate and independent of the inlet port, substantially as described.

M. A furnace havin an intake port, separate air and. fuel supply means discharging into said port, means for preheating the air before it is delivered to said port, and means for utilizing the preheated air to raise the temperature of the fuel before it is mixed with the air, together with a nozzle through which the mixture of air and fuel is dis charged into the furnace chamber, said furnace having an otftalre port which is separate and independent of the inlet port, together with damper means for controlling the inlet and oii'take ports, substantially as described.

15. A furnace having an inlet port, separate air and fuel supply means discharging into said port, means for preheating the air before it is delivered to said port, heat eachanger for utilizing the excess heat of the preheated air to raise the temperature of the fuel lower the temperature of the air, and a chamber and nozzle for effecting the mixture of the fuel and air and a discharge of such mixture into the furnace chamber, said furnace having an offtalre port which is separate and independent of the inlet port, to

gcther with damper means for controlling the oil'take and inlet ports,'substantially as described.

16. A furnace having an intake port, separate air and fuel supply means discharging into said port, means for preheating the air before it is delivered to said port, and means forutilizing the the preheated air to raise the temperature of the fuel before it is mixed with the air, together with a nozzle through which the mixture of air and fuel is discharged into the furnace chamber, said furnace having an otltalre port which is sep arate and independent of the inlet port, together with damper means for controlling the inlet and otl'talre ports, said damper means being movable to alternately close either the intake or the offtake ports, substantially as described.

ii. A furnace having an inlet port, separate air andfuel supply means discharging into said port. means for preheating the air before it is delivered to said port, a heat exchanger for utilizing the excess heat of the preheated air to raise the temperature of the fuel and lower the temperature of the air, and a mixing chamber and nozzle for effecting the mixture of the fuel and air and a discharge of such mixture into the furnace chamber, said furnace having an olftalre port which is separate and independent of the inlet port, together with damper means for controlling the olitalre and inlet ports, said damper means being movable to alternately close either the intake or the ofi'talre ports, substantially as described.

18. A. furnacerhaving fuel and air supply means, means for preheating the air, and a heat exchanger throngs which both the air and the gas pass before their admixture, together "with a mixing chamber and nozzle into which the fuel and air are discharged from the heat exchanger, substantially as described.

19. A furnace having an intalreiport conng of separate air and fuel supply means discharging into said port, and a heat enchan e chamber in which the excess heat of the preheated air is utilized to raise the temperature of the fuel, thereby lowering the temperature of the air, a mixing chamber for ellecting the mixture of the fuel and air, a suitable nozzle for the discharge of such mixture into the furnace chamber, said furnace chamber having an ofitalre port which is separate and independent of the inlet port, together with damper means for controlling the ol'ltalre and inlet port, said damper insane lBll being movable to alternately close either the intake or the ofitake port, and a heat exchanger in which the excess heat of the Waste gases leaving the furnace may be wholly or 5 in part used for the purpose of preheating the air previous to entering the inlet port, together with suitable connecting passages, substantially as described.

In testimony whereof, I have hereunto set 10 my hand.

- "WALTER nn FRIES. 

